(i) Field of the Invention
This invention relates to a novel agent for improving the adhesion of asphalt to aggregate and to the improved asphaltic concrete so formed.
(ii) Description of Prior Art
The use of asphalt in the production of road-making materials is well known. The asphalt material acts as a binder for solid aggregates. Typical solid aggregates which have been employed include stone, gravel and slag.
Road construction has many variations. Asphaltic concrete can be used for the entire road bed or just for the surface. Asphaltic concrete, particularly at the road surface, has considerable advantages over other materials particularly due to its elasticity and compliance. However, the asphaltic concrete does deteriorate with time and heavy traffic. Deterioration can be accelerated due to weakening of the asphaltic concrete due to the stripping of asphalt cement from the aggregate by moisture. One aim of this invention is the improvement of resistance to this stripping.
The quality of the aggregate is also important. A number of materials with appropriate size distribution can serve as aggregates; among these are sand, limestone, slag, lime, vulcanized rubber, or ground and screened coke obtained by any known method from coal or oil. A mixture of aggregates can also be used. The susceptibility to stripping can vary considerably for different aggregates.
An asphaltic cement satisfactory for use as a bonding and coating agent for mineral aggregate should have the following properties: it should be able to coat completely the aggregate; it should have such adhesive qualities that the adhesion between the asphalt and the aggregate is not disrupted in the presence, or because, of water or by variations in climatic conditions; it should provide the pavement with a certain amount of resiliency and a high coefficient of "rehealing"; and it should so resist oxidation that the pavement retains its rehealing characteristic over a long period of time, the ideal asphaltic concrete being one in which the asphaltic cement is as soft as possible and yet has the capacity of resisting being deformed by traffic shocks and impacts.
At this time most of the asphaltic concrete road construction involves hot mixing and paving while the mixture is hot. However, paving can also involve mixtures containing emulsified or cut-back asphalts.
It is well known that asphalt can have poor adhesion to aggregate in the presence of water. Aggregate can be preferentially wetted by water, so that even if the aggregate was dry at the time it was blended with the asphalt, in the course of time the penetration of water into the asphalt composition reaches the aggregate and then interferes with the bond between the aggregate and the asphalt, leading to separation of the asphalt from the aggregate, with resulting breakup of the composition.
Asphalt compositions used in asphalt pavings are viscous semi-solid materials. In order to apply these materials to a surface it is necessary first to convert them to a temporarily fluid state, e.g., by lowering the viscosities by heating or by production of emulsions or by cutting back with liquid hydrocarbons.
The adhesion between asphalt and aggregate is known to be improved by the addition of a basic substance, e.g., an amine, thereto. The result is an increased pavement life.
Examples of some basic additives which have been used in the past for this purpose include the primary alkyl amines, e.g., lauryl amine, stearyl amine, and the alkylene diamines, particularly the alkyl-substituted alkylene diamines, e.g., N-stearyl-1,3-propylene diamine. Amides are also used in some anti-stripping formulations. The production of these additives involves considerable costs.
Many patents have proposed the use of such anti-stripping agents in asphalt/aggregate mixture to provide road surfacing composition.
Canadian Patent No. 425,128 patented Jan. 16, 1945 provided a bituminous bonding material comprising a bituminous material, a solid mineral aggregate and a small quantity of a long chain alkyl amidine, e.g., a compound obtained by the successive action of alcohol hydrogen chloride and ammonia on a high molecular weight alkyl nitrile.
Canadian Patent No. 481,806 patented Aug. 18, 1952 by F. C. Gzemski, provided a method of improving the adhesivity of bitumens to mineral aggregates, e.g., to provide improved road paving compositions. The patentee taught the incorporation in the bitumen of a relatively small quantity of a cyclic nitrogen base sulfonate, (e.g., particularly a pyridinium and quinolinium salts of oil-soluble petroleum sulfonic acids) to increase the wetting power or adhesivity of the bitumens for aggregates.
Canadian Patent No. 986,256 issued Mar. 30, 1976 to M. E. Hellsten et al, taught that the adhesion between asphalt and aggregate would be greatly improved by the addition of a cationic substance, e.g., an amine. The patentee thus provided an asphalt composition having improved adhesion to aggregate comprising asphalt and an amount, sufficient to improve the adhesion of the asphalt to aggregate, of an ether amine having a specifically-recited formula.
U.S. Pat. No. 2,416,134 patented Feb. 18, 1947 by W. W. Allen, provided a road paving bituminous emulsion of the water-in-oil type. Such emulsion included liquified bitumen, an aliphatic amine containing not less than five carbon atoms, and a particularly-defined water insoluble fatty acid soap in colloidal suspension.
U.S. Pat. No. 3,868,263 patented Feb. 25, 1975 by K. E. McConnaughey, provided a method of making a paving composition in which a primary bituminous binder containing an adhesion promoter was mixed with an aggregate. The primary binder was allowed to cure on the aggregate to form a premix of binder-coated aggregate. After such curing, the premix was then mixed with a secondary bituminous binder to form the paving composition.
U.S. Pat. No. 4,325,738 patented Apr. 20, 1982 by H. Plancher et al, provided a bituminous binder composition, including: a bituminous material, and a minor amount of a moisture-damage-inhibiting agent, comprising a high nitrogen content fraction obtained from shale oil.
U.S. Pat. No. 4,765,839 patented Aug. 23, 1988 by D. S. Treybig et al, provided bituminous composition having incorporated therein the reaction product of an organic amine with a substituted nitrogen-containing heterocyclic compound as an anti-stripping agent.
U.S. Pat. No. 3,928,061 patented Dec. 23, 1971 and U.S. Pat. No. 4,038,102 patented Jul. 26, 1977 by M. E. Hellsten et al, each provided asphalt compositions having improved adhesion to aggregate, comprising an alkyl oxyalkylene amine and, optionally, an alkanolamine.
U.S. Pat. No. 2,336,468 patented Dec. 14, 1943 by W. G. Cole et al, provided a process of coating a hydrophilic aggregate with a bitumen emulsifier. The bituminous emulsion contained an alkaline aqueous phase containing glycinin as a stabilizer.
U.S. Pat. No. 3,085,891 patented Apr. 16, 1963, provided asphalt compositions resistant to stripping, consisting essentially of asphalt and a particularly specified substituted oxazoline.